Methamphetamine (Meth) abuse is an epidemic in our nation, for which an effective pharmacotherapy is yet to be developed. Schizophrenics have an increased propensity to abuse stimulants, and this use results in exacerbation of ongoing schizophrenic symptoms and an increased incidence of relapse to (previously controlled) psychosis. The current application is predicated on the idea that therapeutic benefit would be provided in cases of such dual-diagnosis by reducing the motive for drug taking. Anti-dopamine treatments clearly are not sufficient. The metabotropic glutamate receptor group I subtype 5 (mGluR5) is critically . involved in stimulant craving and reward as well as sensorimotor deficits associated with schizophrenia neuropathology;thus, negative allosteric modulators (NAM) for mGluR5'are credible candidates for Meth addiction therapy in the schizophrenic patient. These agents offer greater selectivity and better side effect : profiles than traditional antagonist therapies. The objective of this grant is to determine in rats if NAM-for the mGluR5 should be considered for the treatment of Meth abuse in humans, in particular Meth abuse in schizophrenia. In Aim I a novel paradigm to identify rat model of human dual-diagnosis will be employed. To do so, rats will be subjected to repeated intermittent treatment of amphetamine (or alternatively, phencyclidine) to produce sensorimotor deficits that measured via prepulse inhibition (PPI). PPI scores will then be assessed for "high" and "low" responders. Subsequently, all rats will undergo Meth-induced conditioned place preference (CPP). We predict that high PPI + robust Meth CPP will be considered as a rat model of co-morbidity. NAM of mGluR5 (MPEP, fenobam, or SIB-1757) will be administered after Meth conditioning to determine if the treatment can reduce subsequent testing CPP. The potential for 'normalizing'subsequent PPI also will be determined. For Aim II, immunoblotting approaches will be used to determine if changes in mGluR5 surface expression within limbic regions of the brain are associated with the optimal Aim I paradigm. Focusing on the most likely region, in vivo electrophysiology will be used to determine if surface expression is correlated to efficacy of mGluR5 agonists to alter neuronal activity. Aim III will determine if the strength of glutamatergic transmission and/or neurotransmitter release is altered in co-morbid rats and if this alteration will be normalized with mGluR5 NAM treatment via assessment of paired pulse facilitation of excitatory postsynaptic potentials recorded intracellularly in vivo. We will have not only identified the potential of NAM of mGlurR5 for abrogating Meth-abuse in schizophrenia, but also provided important new insights into the neuronal mechanisms that contribute to this co-morbidity.